A number of systems for supporting pipes and other components from elongated, U-section components variously termed struts and channels have heretofore been proposed. Systems of the foregoing character of which I am aware are disclosed in U.S. Pat Nos.: 1,668,953 issued May 8, 1928, to Erickson for MOLDING FOR ELECTRIC CABLES; 2,273,571 issued Feb. 17, 1942, to Hafemeister for PIPE HANGER; 3,042,352 issued Jul. 3, 1962, to Stamper for PIPE HANGER; 3,132,831 issued May 12, 1964, to Stamper for CLIP-ON PIPE HANGER; 3,226,069 issued Dec. 28, 1965, to Clarke for HANGER FOR CYLINDRICAL CONDUITS AND THE LIKE; 3,527,432 issued Sept. 8, 1970, to Lytle for PIPE OR TUBING SUPPORT; 3,565,385 issued Feb. 23, 1971, to Zurawski for FLUORESCENT TUBE BOX SUSPENSION SYSTEM AND MEANS; 3,650,499 issued Mar. 21, 1972, to Biggane for CLAMP FOR PIPE SUPPORT WITH SLANTING PIVOTAL ASSEMBLY; 4,417,711 issued Nov. 29, 1983, to Madej for PIPE HANGER; and 4,695,091 issued Sept. 22, 1987, to Lindberg et al. for NON-METALLIC STRUT SYSTEM and in a Spring 1987 catalog from Aickinstrut, Inc., P. O. Box 569, Redmond, Wash. 98073.
Systems of the type disclosed in the foregoing patents have been in use for over fifty years to support pipes, electrical raceways, and other system components from the floors, walls, and ceilings of buildings and from other structures. The struts or channels of the system are attached to the structure; and clamps, connectors, and other fittings are employed to attach the supported component (or load) to the channels or struts.
The earlier systems of this type were fabricated from such then available materials as cold rolled steel (see, for example, above-cited U.S. Pat. Nos. 1,668,953 and 2,273,571), and a number of systems of comparable character have been proposed in more recent years (see above-cited U.S. Pat Nos. 3,042,352; 3,132,831; 3,226,069; 3,565,385; 3,650,499; and 4,417,711). These heretofore proposed systems have the decided disadvantage that they offer little resistance to corrosion unless painted or galvanized. Even then, they deteriorate rapidly in aggressive chemical environments, for example in pulp mills and in buildings housing plating tanks. Therefore, as engineering polymers became available, a number of manufacturers substituted those materials for the theretofore employed steels and other metals. To date, this has met with only limited success. This is primarily because the designers of non-metallic support systems have not taken into account the physical differences between the non-metallic and metallic materials they employed. Of particular significance in this respect are the typically quite different coefficients of friction of the metallic and non-metallic materials employed in systems of the type under discussion.
Specifically, in a typical, heretofore proposed system with metal components, there is a simple frictional fit between the supporting strut or channel and the fixture installed in that channel to support a load from it (see, for example, above-cited U.S. Pat. Nos. 3,226,069; 3,527,432; 3,565,385; 3,650,499; and 4,417,711). With non-metallic, engineering polymers substituted for the theretofore utilized metallic components (see, as an example, above-cited U.S. Pat. No. 4,695,019) this approach proves somewhat less than satisfactory. Due to the much lower coefficients of friction, the load-supporting fixture can easily slip along the supporting strut or channel when a polymer is substituted for metal in a conventional support system design, allowing the load to shift. This is especially true in applications in which the supporting channels are vertically oriented, particularly if the load is relatively heavy or subjected to vibration or hammering and because the pipe runs are often then employed as ladder rungs. Shifting loads are of course very undesirable as they radically increase the potential for system failure.
The use of stop blocks in the load-supporting channel or a complicated channel and fixture arrangement with extended continuous contact therebetween (see above-cited U.S. Pat. No. 4,695,019) to increase the fixture-to-channel contact area and therefore increase the friction between these system components and minimize slippage of the supported load has heretofore been proposed. This approach is, however, not without its disadvantages. Perhaps the most important of these is that the average installer must be reeducated and his resistance to employing a non-conventional system with an additional component overcome. Secondly, available stop blocks are relatively expensive; and large numbers of these components (typically four per foot) are required, Therefore, in a typical installation, systems employing stop blocks are not competitive unless corrosion problems are severe and support systems with metallic components can not be employed. Finally, and as a corollary, systems with stop blocks are typically not competitive because of the additional labor required to install a system of that character.
Another approach to preventing slippage that is suggested in the prior art is to notch the side walls of the U-sectioned supporting channel and to install the load connecting system components in these notches so that the fitting cannot slip relative to the channel, even if the latter is vertically oriented. The above-cited Stamper U.S. Pat. Nos. 3,042,352 and 3,132,831 disclose systems of the just-described character. Again, however, the heretofore proposed system is not one which would be satisfactory if channels fabricated of engineering polymers rather than metal components were employed to get the corrosion resistance and other benefits of those non-metallic materials. Specifically, the slots or notches in the Stamper channels leave lips or ears of very small section on which the supported load is imposed. In applications involving heavy loads or vibration, these lips would be very apt to fail, resulting in system failure. If an engineering polymer with its lower shear strength were substituted for steel in Stamper's systems, this tendency would be many times aggravated and the substitution would produce a system of little if any value.
Furthermore, failure of one load will often have a domino effect with adjacent loads failing until the entire system or a large section of it has been destroyed. Thus, the heretofore proposed support systems have the important drawback that they are unable to prevent such catastrophic failures.
Another salient disadvantage of the Stamper systems is that it would be extremely difficult, if possible at all, to connect cross channels between parallel horizontal or vertical runs. Ths side walls of the Stamper systems are so thin, in this respect, that it would not be practical to support a cross-channel of the Stamper type from the side walls of a normally extending channel as would be required to connect those channels together. Thus, as a grid of supporting channels is typically required, the applications in which the Stamper systems would be useful are extremely limited.
Still Another disadvantage of the Stamper systems is that no provision is made for retaining a channel nut or other fixture component in the load-supporting strut. This is a significant drawback as channel nuts and the like can be employed to advantage in attaching connectors and other fittings via which one channel may be connected to a cross channel and also via which a variety of different load devices may be attached to a channel. Modifications of the Stamper channels which would allow the use of channel nuts and the like would be impractical because the channel configurations required to retain such devices would increase the cost of the channels to the point where the system would become economically non-competitive if they were rendered in metal.